Cathode ray display systems

ABSTRACT

Improvements for cathode ray tube character displays are disclosed, using the same magnetic yoke deflection system for X-Y character location and character scan, the latter including a high frequency raster scan, for example, in the Y-direction. The hf raster scan control is coupled to the Y-deflection yoke system for resonance at the raster scan frequency.

United States Patent McVey et al. 1 Jan. 16, 1973 [541 CATHODE RAY DISPLAY SYSTEMS 3,4l8.5l9 12/1968 Ferricr, Jr. ct al .315/24 x [75] Inventors: Irvin M. McVey, Agoura; Norman Olson, Marina Del Rey. both of Primary Examiner-Carl D. Quarforth Cafifl Assistant Examiner-J. M. Pote'nza An S th, R t & P n [73] Assignee: Xerox Corporation, Stamford, omey my Os on av] 57 ABSTRACT F' [22] Aug Improvements for cathode ray tube character displays 1 PP N04 349,992 are disclosed, using the same magnetic yoke deflection system for X-Y character location and character scan, [52 0.5. CI ..315/18, 315/24 the latter including a high frequency raster Scan, for [5 l] Int. Cl ..H01j 29/70 p n h irection. The hf raster scan control [58] Field of Search ..3l5/l8, 24; IMO/324.1 is coupled to the Y-deflection yoke system for resonance at the raster scan frequency. [56] References Cited 7 Claims, 3 Drawing Figures UNITED STATES PATENTS 3,336,497 8/l967 Osborne ..3I5/l8 i Jame 0 32 J1 X- Genera/0r 30 far/W0 M 10 /am e ramlra/ J6 6 1a '5 ll 21 25 93! 25 24 #42 l drrfl/a/or II [43 Z5 c'fiaracler 26 award/0r 44 1 CATHODE RAY DISPLAY SYSTEMS The present invention relates to improvements in cathode ray tube display systems, and more particularly to the control of cathode ray tubes when used to display message texts composed of alpha numerical characters or to display geometric lines, curves, or the like.

Display devices of this type constitute a special input/output equipment for digital computers in that in accordance with a particular computer output program, the result of that computation program is displayed. More particularly, the display device is usually provided with a keyboard to provide a direct man-computer dialog facility. Visual presentation of the result may take the form of alpha-numerical characters similar to regular text print-out; alternatively, the result may have to be presented as a graphic display of geometric configurations. in order to facilitate such a display covering the entire display area or a substantial portion thereof, the information to be displayed is broken down into basic, small size configuration elements or components, such as the letters of the alphabet and numbers, or basic geometric design units, such as short lines of particular direction, curvature or the like. Each such elemental display component will be called a character, and it is presumed that a particular plurality of such different characters can be defined and established to be used to compose large scale information for display.

The display of extensive information by way of composition from elemental components (characters) requires (1) to generate the basic characters, (2) to place the basic characters in a particular location in the display area, and (3) to selectively control this generation and placement process for composite display of large scale, multi-character information. From a different point of view and considering particularly that a display tube of the cathode ray type is to be used, the information display requires the electron beam to be deflected such that it generates repeatedly a particular character in a particular area on the display tube screen.

Generation of visible characters in different areas of the display screen, in rapid sequence and on a repetitive basis causes the composite information to be displayed as long as desired. Hence, for the display of a particular character within such composite information display, it is required to select a particular incremental area on the display tube screen, to select a particular character and to control the electron beam to generate the selected character in visible form in the selected incremental area on the screen. These two different but associated selections and control operations are made on the basis of signals provided as input signals for the system. These input signals may be derived from a computer which assembles the information accordingly for display.

The display area can be thought of as being subdivided into a multitude of such incremental areas. The location of a particular character within a composite display can be regarded as being given by a pair of coordinates defining the location of an incremental area. In other words, the computer provides signals identifying by way of coordinate values one of the plurality of incremental areas available on the screen and into which a character is to be written or drawn. The electron beam of the cathode ray tube must thus be deflected in accordance with such a pair of coordinate values, defining, however, specifically only one point (e.g., center or comer) of the particular incremental area.

After selection of the location of a particular incremental area in which the character is to be displayed, the incremental area is raster scanned, and the particular character is generated visibly by appropriate cathode ray intensity controls during the raster scan. This raster scan thus covers the selected particular incremental area, for example, in a line for line scan.

The composite information will thus be displayed by subjection the electron beam sequentially and stepwise to deflection for sequentially selecting all of the various incremental areas on the display screen and in accordance with XY coordinate signals sequentially provided by the computer. For each such pair of coordinate signals, a raster scan of the particularly associated incremental area is provided, and by covering the entire display area in this manner, large scale composite displays are produced.

The sequence of coordinate signals, as provided by the computer, is, of course, accompanied by a sequence of character-defining signals, and during the raster scan of each incremental area the desired character is written by the electron beam within that incremental area. The scan of the entire display area, i.e., the display of all characters pertaining to a composite display field, must be completed at about TV frame time, or shorter, to be repeated at that rate or at a comparable rate commensurate with flicker free display.

it is apparent from the foregoing that the selection process of incremental areas is fast relative to the repetition rate of the display frame, but it is slow relative to the raster scan within each incremental area. In reality, the raster scan requires scanning frequency up to or even above the megacycle range. Operational requirements for the two types of selections are thus different as to speed and response. Selection of the lo cation of an incremental area on the screen requires relative large displacement distances to be traversed, but at not too high a speed compared with the raster scanning speed for character generation. In other words, position control for selecting the location of an incremental area does not have to be too fast in comparison with the raster scan, but it must cover the entire display screen and, therefore, must be responsive over a wide dynamic range of input signals and must provide accordingly a high gain for these input signals. The raster scan is very fast but covers only small distances as during each scan only the small dimension of an incremental area has to be covered by the scan.

It has been common to use a magnetic yoke type deflection system for the XY location of an incremental area in order to avoid utilization of excessively high deflection voltages needed in electrostatic deflection systems when covering a wide screen. A drive amplifier for an electrostatic deflection system, ultimately having logic signals derived from the computer as inputs, would have to have extremely high gain and over a wide dynamic range with high output voltages. A magnetic yoke system, though comparatively slow, has sufficient speed and response for the Xy location even if the operating voltages provided by the deflection control amplifier are comparatively significantly lower than for an electrostatic system.

conventionally, the raster scan is carried out by a faster operating, additional electrostatic deflection system now covering only small deflection angles but at a rapid rate; the deflection voltage range needed here is thus comparatively small. While meeting deflection speed requirements at reasonable operating voltages for the drive amplifiers in these two different type of deflection systems, the employment of dual deflection system poses other problems.

The' characters to be written by the electron beam on the display screen should have similar appearance re gardless of the location on the screen. If the characters are basic geometric line increments, such similarity is critical, otherwise the overall graphic and geometric display will be distorted and will appear to have gaps, interruptions, etc. If the characters are letters or numbers,'distortions of any kind or tilted placement, are at least annoying. In case of a dual deflection system, as mentioned, it is necessary to place the deflection yokes and the deflection electrodes in spaced apart relationship along the propagation path of the electron beam in the CRT. Thus, the beam deflection for location definition and the beam deflection for raster scan occur at different points along the beam. This results in distortions of the display, particularly characters displayed in the corners of the screen are tilted. One way of combating this distortion is to generate the same character during the raster scan differently for differently located incremental areas. However, this is extremely uneconomical.

It is an object of the present invention to solve the problem of character distortion in a different manner. The solution was found to actually simplify the system in that only a single deflection system is needed rather than a dual system as used heretofore and generating the problem sought to be resolved.

In accordance with the invention, it is suggested to use a magnetic yoke deflection system for both, XY position and for raster scan. Separate amplifiers are used for the position and raster scan control whereby the raster scan amplifier is capacitively coupled to deflection coils such that there is resonance with the induction of the coil system at raster scan frequency. Hence, the raster scan drive is operated at the frequency for which its output circuit has minimum impedance.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawing in which:

FIG. 1 illustrates schematically a keyboard display improved in accordance with the vendor;

FIG. 2 illustrates somewhat schematically a block and circuit diagram for the preferred embodiment for practicing the present invention; and

FIG. 3 illustrates an enlarged portion of the display tube screen to facilitate orientation and description.

dividual characters, either for immediate display or to provide substitute symbols or the like for editing of text, or, in general, as input for communication with a computer responding to such input by causing a response to be developed on screen S.

Turning now to FIG. 2, there is shown a display tube 10 of the cathode ray type as provided for display of large area information on its screen S. This information to be displayed is assumed to be composable of individual characters. Identification of the characters to be displayed are held as digital data in a cyclically operated storage facility 11. The storage facility 11 presents all data to be displayed once per display frame cycle. The frame rate may be, for example, 50 frames per second for flicker free viewing.

Storage device 11 receives the data to be displayed from any suitable source, such as a digital computer 12. The data is updated from the computer or otherwise whenever needed. However, this aspect of transfer of data into and out of storage device 11 is not part of the present invention, and it is merely assumed that the data to be displayed are regularly available in the storage device 11 and are cyclically presented by it for display. The storage device 11 has a pair of plural line output channels 13 and 14. Signals in representation of the XY coordinates for a particular area increment on display screen S are presented in channel 13; signals in representation of the identification of characters to be displayed are presented concurrently in channel 14.

Channel 13 connects to an XY position control circuit 15 which can be thought of as being a digital-toanalog converter. The position defining signals are stored in the facility 11 in digital form, and they have to be translated into (analog) deflection control currents for the CRT 10. Position control 15 has two output channels 16 and 17 respectively for the X and Y deflection signals. In particular, channel 16 receives an analog signal from circuit 15 in representation of the vertical deflection defining, for example, at a low signal level, the center Yrn of a line on the screen in which characters are displayed. (See FIG. 3)

A power amplifier 18 is connected to channel 16 to amplify the low level Y-position signal to provide a current output for operating a Y-deflection yoke 20 which includes coils 21 and 22 connected in series and in between the output channels or amplifier 18. Hence, in response to an input signal applied to amplifier 18, a current flows through coils 21 and 22, causing the electrode beam in CRT 10 to impinge on target screen S thereof at vertical position Ym, defining the vertical center of an incremental area onto which a character is to be written for display. The entire area increment may extend in the vertical direction by Ym i-AY, so that 2AY defines the height of a character to be displayed on screen S of CRT 10.

An X coordinate signal is presented by control 15 as low level signals in channel 17 and concurrently with the Y-coordinate signal in channel 16. The system includes a horizontal deflection system 30 with a coil system 31 connected to a power amplifier 32 for providing suitable deflection current to the coil 31. The

particular X-coordinate signal presented by control at any instant defines the position of a character in any line and may define, particularly, the X-coordinate of the left-hand side of the area increment in which a character is to be displayed. Thus, after suitable amplification of such signal in amplifier 32, the electron beam is deflected to intersect target and display screen S at, for example, coordinate Xi. (See FIG. 3)

The equipment as designed thus provides deflection of the electron beam to intersect display screen S at a point Xe, Ym defining the position of a character and being at the incremental area into which the character is to be written. Xi is of course but one of the plurality of different X-values possible, the number of possible values being equal to the number of characters per line, and Ym is one of the plurality of different Y-values, the plurality being equal to the number of lines of characters which can be written on the screen.

For display control of the character, i.e., for the visible generation thereof, the incremental area has to be raster scanned, again in two directions. The raster scan in one direction can be comparatively slow and it is not that direction where the scanning presents speed problems. For the slow component of the raster scan, the X direction has been selected, which is basically arbitrary. Therefore, channel 17 is not directly coupled to the input of amplifier 32. Instead, there is interposed a sweep generator 33 algebraically adding a sweep signal to each newly presented position signal forming the X coordinate. The sweep generator 33 provides a sweep signal to be added to the X-coordinate signals applied to the input of amplifier 32, varying basically from zero to a value which after due amplifications in the system 30 covers the width AX in X direction of an incremental area anywhere on screen 8.

It follows that as a new pair of XY signals is presented by control device 15, the horizontal deflection control 30 causes the beam to shift to a coordinate such as, for example, Xil under control of the specific X coordinate signal applied by channel H7 in analog form to amplifier 32 and with zero sweep amplitude provided at that moment. The sweep device 33, which is a sawtooth oscillator or the like, is triggered thereby to provide a progressively increasing signal added to the X1 signal in channel 17 until retracing, thereby a deflection in X direction is produced on screen S of CRT it), ranging from Xil to Xll +A X, as AX is the width of an incremental area anywhere on the display screen. The sweep period of generator 33 is precisely equal to the period it takes to write a character on the screen. The corresponding raster scan in Y-direction is provided as follows:

An oscillator provides a signal having frequency of the required vertical raster scan. This frequency may be in the m'egacycle range, such as 0.93KHZ. A drive amplifier 23 is connected to oscillator 25 to receive this signal and feeds an amplified replica thereof to a series circuit comprised of a capacitor 24 and of the primary winding 26 of a transformer 27. The secondary winding 28 of the transformer interconnects the two coils 2i and 22. Therefore, an EMF is added centrally to the drive voltage for the two coils 211 and 22 (as derived from amplifier 18) and whenever the transformer developes a voltage in its secondary circuit.

The capacitor 24 is now selected such that there is series resonance with the inductance of the entire system 21, 22 and 26, as reflected to the primary circuit of the transformer, at the frequency of oscillator 25. Thus, the output circuit of amplifier 23 has minimum impedance at raster scan frequency. The transformer turns ratio is chosen to obtain proper voltage at the vertical winding to obtain the desired vertical character scan covering the 2AY amplitude of a given yoke inductance and sensitivity.

it should be noted that the vertical deflection system has its own resonance frequency by operation of the inherent capacitance thereof. Capacitor 24 thus serves as a tuning element. in effect, the capacitor lowers the inherent resonance frequency of the yoke system. Therefore, the inherent capacitance of the yoke system deflection must be such that the inherent resonance frequency of the yoke system is higher than the raster scan frequency. This, however, will not present any problem as raster scan frequencies are generally lower than the inherent resonance frequency of CRTs usable for display purposes. Nevertheless, it can be seen that in case the raster scan frequency can be and has been seiected to be at least approximately equal to the resonance frequency of the Y- yoke system, a capacitor may not be needed. it is merely essential that the raster scan frequency is the resonance frequency, or very close to it of the output circuit of raster drive amplifier 23. Moreover, the capacitor can 'be regarded as being included in the Y- yoke deflection system to establish a particular resonance frequency of that system.

in order to complete description of the system, channel 114 receives a signal identifying a particular character to be displayed in the incremental area defined by the currently provided position signals in channel l3. A decoder 40 receives these character defining signals and controls a character generator 41, such as a monoscope or the like. The character generator 411 has an output channel 42 which provides a train of control signals to CRT lit to control the beam intensity therein.

As schematically indicated by lines 43 and 44, the character generator M is operated in phase synchronism with the raster scan signal as derivable from oscillator 25 for vertical raster scan and from sweep generator 33 for the horizontal raster scan. The output signal of generator 411 thus represents the beam intensity in CRT Mi for the continuing raster scan, to enable the beam to write the desired character on the screen within the area defined by the location signal and covered by the raster scan as described below.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.

We claim:

ll. lln a system for the display of data which includes a cathode ray tube with a magnetically operated deflection system, the system including means to provide first signals in representation of characters to be displayed for controlling the intensity of the cathode ray beam in the tube and still further including means to provide second signals concurrently with the first signals and defining the location of the character to be displayed on the screen of the tube, the improvement comprising:

first amplifier means responsive to particular ones of the second signals, defining the beam deflection in a first direction and connected for controlling the system as to beam deflection in the first direction;

first means for providing oscillations at raster scan frequency in the first direction to be used for character generation;

second amplifier means connected to the first means to receive the oscillations; and

second means coupling the output of the second amplifier to the beam deflection system for deflection in the first direction and for resonance therewith at said oscillation frequency.

2. In a system as set forth in claim 1, the deflection system for deflection in the first direction including a pair of coil means connected in series and interconnected by the second means to develop an EMP between the coil means representative of the resonance oscillations.

3. In a system as set forth in claim 1, the deflection system for deflection in the first direction including a pair of coil means, the second means including a transformer having a secondary winding interconnecting the coil means of the pair to form series circuit therewith, the transformer having a primary winding, the second means further including capacitive means connected to the primary winding, the second amplifier connected to the primary winding and to the capacitive means.

4. In a system for display of information on the screen of a cathode ray tube having. a deflection system, the deflection system for deflection in one direction including a magnetic yoke system, the combination comprising:

first means for generating character signals for control of the cothode ray tube for the display of characters in selected locations of the display screen of the tube, and including means to provide signals for raster scan of character generation and display control;

second means for providing signals in representation of deflection of the cathode ray in the tube to identify a particular location on the display screen; and

third means for connecting the first and second means to the deflection system of the tube, the third means and the yoke system or the deflection system for deflecting the beam in the one direction of the raster scan with resonance at the raster scan frequency.

5. In a system as set forth in claim 4, the second means including fourth means to provide electric energy in representation of location signals to the deflection system including particular signals for operation of the deflection system for deflection of the beam in the one direction;

the third means including fifth means connecting the first means to the deflection system so that an emf in representation of the raster scan signal is superimposed upon the electrical energy as provided to the deflection system by the fourth means for deflection in the one direction.

6. In a system as set forth in claim 4, the third means including a capacitor to establish a particular resonance frequency tcggethe r with the yoke s stem.

7. In a system as set orth in claim 4, the yo e system including biparted coil means interconnected through a transformer included in the third means, there being oscillation means included in the first means connected to the transformer for providing oscillation voltages to be effective between the coil means. 

1. In a system for the display of data which includes a cathode ray tube with a magnetically operated deflection system, the system including means to provide first signals in representation of characters to be displayed for controlling the intensity of the cathode ray beam in the tube and still further including means to provide second signals concurrently with the first signals and defining the location of the character to be displayed on the screen of the tube, the improvement comprising: first amplifier means responsive to particular ones of the second signals, defining the beam deflection in a first direction and connected for controlling the system as to beam deflection in the first direction; first means for providing oscillations at raster scan frequency in the first direction to be used for character generation; second amplifier means connected to the first means to receive the oscillations; and second means coupling the output of the second amplifier to the beam deflection system for deflection in the first direction and for resonance therewith at said oscillation frequency.
 2. In a system as set forth in claim 1, the deflection system for deflection in the first direction including a pair of coil means connected in series and interconnected by the second means to develop an EMP between the coil means representative of the resonance oscillations.
 3. In a system as set forth in claim 1, the deflection system for deflection in the first direction including a pair of coil means, the second means including a transformer having a secondary winding interconnecting the coil means of the pair to form series circuit therewith, the transformer having a primary winding, the second means further including capacitive means connected to the primary winding, the second amplifier connected to the primary winding and to the capacitive means.
 4. In a system for display of information on the screen of a cathode ray tube having a deflection system, the deflection system for deflection in one direction including a magnetic yoke system, the combination comprising: first means for generating character signals for control of the cothode ray tube for the display of characters in selected locations of the display screen of the tube, and including means to provide signals for raster scan of character generation and display control; second means for providing signals in representation of deflection of the cathode ray in the tube to identify a particular location on the display screen; and third means for connecting the first and second means to the deflection system of the tube, the third means and the yoke system or the deflection system for deflecting the beam in the one direction of the raster scan with resonance at the raster scan frequency.
 5. In a system as set forth in claim 4, the second means including fourth means to provide electric energy in representation of location signals to the deflection system including particular signals for operation of the deflection system for deflection of the beam in the one direction; the third means including fifth means connecting the first means to the deflection system so that an emf iN representation of the raster scan signal is superimposed upon the electrical energy as provided to the deflection system by the fourth means for deflection in the one direction.
 6. In a system as set forth in claim 4, the third means including a capacitor to establish a particular resonance frequency together with the yoke system.
 7. In a system as set forth in claim 4, the yoke system including biparted coil means interconnected through a transformer included in the third means, there being oscillation means included in the first means connected to the transformer for providing oscillation voltages to be effective between the coil means. 